We wish to explore the properties and regulation of two newly discovered K channels in lateral membrane of principal cell (PC) of mammalian cortical collecting duct (CCD). Basolateral K channels participate in the generation of cell membrane potentials, in recycling of K across the basolateral membranes and they serve as a second route of K entry into cells at high aldosterone levels. In preliminary experiment, I have identified two novel types of K channels, a low-conductance K channel and an intermediate-conductance K channel in PC lateral membranes. Little is known about the properties and the regulation of these K channels. I propose now to: 1) characterized these K channels, 2) to study their regulation, 3) to explore effects of hormones. To achieve the first goal, both cell-attached and inside-out patches will be used to study single channel kinetics, channel open probability, gating mechanisms, ion conductances and channel selectivity to Na+, Rb+, NH+ and Cs+ of both populations of K channels. The effect of changes of cell pH on channel activity will also be investigated. K channel blockers such as Ba2+ and TEA will be screened and their blocking mechanisms explored. To achieve the second goal, I will attempt to answer the following questions: 1) Is the lateral K channel sensitive to ATP and other nucleotides? 2) Is channel activity modulated by phosphorylation and dephosphorylation and mechanisms mediated by the cAMP-dependent protein kinase (PKA), protein kinase C (PKC) and Ca/calmodulin-dependent kinase? 3) What kind of role does phospholipase A2+ arachidonic acid and the related metabolites play in channel regulations? 4) Are guanine nucleotide-binding proteins (G-protein) involved in the regulation of channel activity? To achieve the third goal, I will study the effect on channel activity of three maneuvers that alter Na reabsorption and K secretions. These will involve investigation of channel activity following the administration of mineralocorticoid, vasopressin and modulation of basolateral Na-K ATPase activity. The role of several cellular second messengers pathways in channel modulation will also be investigated. Finally, we propose to intergrade our results with the current concepts of distal nephron K secretion and NA reabsorption.